The goal of this project is to determine the feasibility of developing inhibitors of the Staphylococcus aureus multidrug-efflux transporter NorA. NorA provides S. aureus with intrinsic resistance to fluoroquinolone antibiotics by reducing their concentration inside the bacterial cell. Inhibition of NorA has been demonstrated to dramatically potentiate the antibacterial action of fluoroquinolones and prevent the emergence of antibiotic-resistant variants of S. aureus. One NorA inhibitor 1 reserpine, has already been identified by the authors. Unfortunately, the use of reserpine is limited by its neurotoxicity. Preliminary studies have demonstrated that reserpine is not unique in its ability to inhibit NorA; screening of 2,500 organic compounds has yielded a number of structurally diverse molecules also capable of suppressing NorA activity. During the first, exploratory phase of the project, 7,500 more compounds will be screened for their ability to inhibit NorA. To eliminate toxic compounds, the identified inhibitors will be tested for their toxicity to a panel of human cell lines. The compounds to which NorA can become insensitive through mutations will also be eliminated. The remaining inhibitors of highest potency will be used in Phase Il of the project as lead compounds, on the basis of which we expect to develop a clinically useful NorA inhibitor. PROVIDE COMMERCIAL APPLICATIONS This project is to develop nontoxic inhibitors of the S. aureus multidrug transporter NorA, the protein involved in resistance of these bacteria to fluoroquinolone antibiotics. The envisioned commercial product is a combination of such an inhibitor with fluoroquinolone. Given that staphylococcal infections are widespread and rapidly become resistant to antibiotic therapy, the market for this product is likely to be comparable to the market for major antibiotics.